1. Field of the Invention
This invention relates to expander type prime movers and more particularly vane type rotary expanders.
2. Description of the Prior Art
In the past, most multivane rotary expanders (hereafter called expanders) have used a compressed gas such as low temperature air as a motive fluid. See for example Machine Design for Sept. 14, 1972, page 218. As this article points out, there are definite limitations in achieving increased torque in such an expander.
Using as the motive fluid a high temperature and high pressure vaporized liquid such as water or hydrocarbon fluids, while increasing the possible power for an expander of a particular size, introduces unusual problems because of the attendant increases in temperature and pressure. One such problem is internal leakage of the vapor. Ideally, when the vapor is introduced between adjacent vanes it will be confined in this space by the rotor, casing and the endwalls. In practice, however, the vapor escapes from between the vanes, when it is admitted shortly after top dead center, to the low pressure region before top dead center. The pressurized vapor tends to force the following vane down into the slot and blow by it back to the exhaust port. The vapor also tends to flow around the ends of the rotor back toward the exhaust ports and radially inward to flow along the shafts to the low pressure exhaust manifold.
One proposed solution to this problem involves admitting the high temperature and high pressure vapor at the base of the vane slot so that the pressure helps to force the vane outwardly (see copending patent application Ser. No. 536,090, filed Dec. 24, 1974). Vapor then proceeds radially outwardly in passages behind the vanes.
An additional problem existed, however, in a prototype being developed, since for lubrication purposes oil was mixed with the vapor which cooled the vapor and heated the oil.